1. Field of the Invention
The present invention relates to a hologram recorder/player for recording holograms in a hologram recording medium and replaying holograms recorded in the hologram recording medium.
2. Description of the Related Art
A conventional hologram recorder/player is disclosed in JP-A-2003-76256 for example. This hologram recorder/player uses so called angle multiplex method for recording a hologram (page data) per page in a hologram recording medium. When the hologram is recorded, the hologram is stored in parts in a page which serves as a unit recording region divided into a central region and peripheral regions, and by re-arranging only the peripheral regions, the two-dimensional rectangular hologram is converted into a circular or an n-sided polygonal shape for recording. This arrangement minimizes image distortion caused by optical system components such as lenses when the hologram is reproduced, and therefore reduces information loss at the time of replay.
However, while the above-described conventional hologram recorder/player deals with hologram image distortion caused by optical components, it does not deal at all with hologram image distortion caused by other factors such as thermal shrinkage of the medium at the time of laser beam application and change in the wavelength. Shrinkage of the medium or change in the wavelength can disable detection of replay beams for some parts of the hologram recorded in the unit recording region even if laser beam application conditions for the replay (such as the incident angle of the reference beam) are exactly the same as those for recording. There is a risk, therefore, that the hologram is not replayed accurately in its entirety. Other problems with the above-described conventional hologram recorder/player include signal loss at borderline areas when re-arranging is made at the time of replay, and detection of unintended signals which are recorded at different angles other than the intended angle.